Gaseous electric discharge device



Oct. 31, 1939.

H. KREFFT El AL GASEOUS ELECTRIC DISCHARGE DEVICE Filed DeC. 10,. 19:55

INVENTORS Hermann KrewPC Kur'b Larclne v Max Thomas ATTORNEY Patented Oct. 31, 1939 UNITED STATES GASEOUS ELECTRIC DISCHARGE DEVICE Hermann Krcflt, Berlin-Friedrichshagen, Kurt Larch, Berlin, and Max Thomas, Weisswasser, Germany, assignors to General Electric Company, a corporation of New York Application December 10, 1935, Serial No. 53,794 In Germany December 12, 1934 3 Claims.

The present invention relates to gaseous electric discharge devices generally and more particularly the invention relates to such devices the gaseous atmosphere of which consists of or comprises a metal vapor, such as mercury vapor.

In certain types of such devices the energy input and the heat dissipating characteristics of the container are in such relation that the container is at an elevated temperature and the O mercury vapor is at an elevated pressure, such as atmospheric pressure during the operation of the device. One type of device of this kind is provided thermionic electrodes and has a starting gas therein, such as argon, krypton, 5 xenon, or neon. Such devices are efficient sources of visible light and emit in addition'ultra-violet light which is useful in therapy, photochemistry, sterilization, irradiation of foodstuffs or the like. When desired, a luminescent material, such as a fluorescent or a phosphorescent material, is associated with the device to transform the ultra-violet light into visible light which complements and supplements the visible light emitted by the discharge in the device. Container glasses which are highly heat resisting, chemically inert with respect to the hot, ionized metal vapor and which transmit ultraviolet light are desirable for use in such devices. Such glasses are not readily attainable, however, and we have observed that glasses which have a high transmission characteristic for ultraviolet rays age rapidly when subjected to such rays of shorter wave length. Further these ultra-violet transmitting glasses have too low a softening temperature and are not inert to the hot mercury vapor and to other hot metal vapors which may be present in the lamp, such as caesium, cadmium, or zinc vapor. On the other hand glasses which are inert tosuch metal va- 0 pors and which have a high softening temperature do not transmit enough ultra-violet at the thicknesses required in lamp containers tomake the lamp useful as an ultra-violet generator.

The object of the present invention is to providea container for a gaseous electric discharge device the gaseous atmosphere of which consists of or comprises a metal vapor which container is capable of withstanding an elevated ticular description. 1 1

In accordance with this object of the inventionthe container comprises two layers of glass which 0 are fused together and which are of different Still furvice and to its use and operation will be apparent to those skilled inthe art from the following parthickness. The inner layer is thinner than the outer layer and consists of a hard glass which has a high softening temperature, about 700 C. or higher, is inert with respect to the hot metal vapor in the lamp and which transmits the ultraviolet rays of the long and medium wave length but which does not transmit the ultra-violet rays of short wave length. The thicker outer layer of the container consists of a glass having a lower softening temperature, about 550 to 600 C., which is attacked by the hot metal vapor and which transmits a large percentage of the ultra-violet rays of long, medium and short wave length but which rapidly deteriorates under the influence of the ultra-violet rays of short wave length. A container of the above structure is useful in connection with gaseous electric discharge devices which operate with elevated container temperatures, such as a temperature of 500 C., and which emit ultra violet light.

In the drawing accompanying and forming part of this specification an embodiment of the invention is shown in aside elevational partly sectional view.

Referring to the drawing the gaseous electric discharge device comprises an elongated tubular container consisting of two glass layers I and, 2 the outer layer I being greater inthickness than the inner layer 2. Said container I has two thermionic electrodes 3 and 4 sealed therein at the ends thereof and a starting gas therein, such as argon, neon or krypton, or a mixture of such gases. Said container I, 2 has a quantity of vaporizable metal therein, such as mercury, the vapor of which emits visible and ultra-violet light during the operation of the device. Preferably the quantity of metal is such that it is wholly vaporized at the operating temperature of the container I, 2. of a metal filament, such as a tungsten filament, wrapped around a bar of electron emitting material, such as a sintered bar of barium, or strontium oxide, or a mixture of such oxides, and is electron emitting when heated. Said electrodes are heated to an electron emitting, discharge supporting temperature directly by the discharge current flow therethrough.

The inner glass layer'2of said container I, 2 preferably consists of a glass having the following composition;

Per cent Silica. (Sloan; 58 Boric oxide (BzO3) 1 Alumina .,(Alz03) Magnesium oxide (MgO 8 Calcium oxide 3aO) i 5 A glass having the above composition has a softeningtemp'erature of about 720 to 740 C., trans The electrodes 3 and 4 consist mits ultra-violet rays ofwthe long" and mediumy Per cent Silica (SiOz) 50 Boric oxide (B202) 1 Alumina (A1203) 5 Magnesium oxide (MgO) 8 Calcium oxide (Ca) 6 Barium oxide (BaO) Phosphorous pentoxide (P205) 5 This glass has substantially the same characteristics as the glass given in the above example.

The outer glass layer 1 preferably consists of a glass having the following composition:

Per cent Silica (SiOz) 74 BOIiC oxide (B203) Sodium oxide (NazO) 7 Alumina (A1203) 4 A glass having the above composition has a softening temperature of about 540 to 560 C. and transmits ultra-violet rays of long, medium, and short wave length at thicknesses in the order of 0.7 mm. or more.

When desired a glass having the following composition is used as the outer layer I:

. Per cent Silica (SiOz) 75.5 Boric oxide (B203) 13. 5 Sodium oxide (NazO) 9 Alumina (A1203) 2 This glass has substantially the same characteristics as the glass disclosed above for use as the external layer I.

Due to the fact that the inner glass layer 2 does not ,transmit the ultra-violet rays of short wave length after the device has been operat- .ing* for a short time the glass of the outer layer I does not age rapidly and remains pervious to the long and medium ultra-violet rays generated by the discharge and transmitted by the inner layer for a long time. The outer layer l'does not become brown or black since it is protected from the deleterious chemical eifects of the hot, ionized metal vapor by the inner layer 2.

The gaseous electric discharge device is useful as an ultra-violet generator and the ultra-violet light emitted thereby is useful for many purposes as pointed out above. When desired, a luminescent material is associated with the device which transforms the ultra-violet light into visible light to complement and supplement the spectrum of the visible light emitted by the device. Such luminescent materials as calcium tungstate, or zinc silicate are useful for this purpose.

When desired the container I, 2 is mounted in an evacuated, sealed envelope which reduces the heat losses therefrom to increase the emciency thereof. The luminescent'material is applied to, or incorporated in said envelope, when desired.

while we have shown and described and have pointed out in the annexed claims certain novel features of the invention, it will be understood that various omissions, substitutions and changes in the forms and details of the device illustrated and in its use and operation may be made by those skilled in the art without departing from the broad spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A gaseous electric discharge device comprising a container, electrodes sealed therein, a gaseous atmosphere therein, and a quantity of vaporizable material therein which emits visible and ultra-violet light when excited to luminescence by an electric discharge between said electrodes, said container consisting of two glass layers fused to each other, the inner layer being thinner than the outer layer and consisting of an aluminate, hard glass inert to said vaporizable material having a softening temperature of about 700 C. and which transmits ultra-violet rays at a wave length of 280 millimicrons and longer and which is opaque to ultra-violet rays of shorter wave length, the outer layer consist ing of a borosilicate glass having a softening temperature of about 550 C. and which transmits ultra-violet rays at a wave length of 280 millimicrons and longer and ultra-violet rays of shorter wave length and which is deleteriously affected by said rays of shorter wave length.

2.,A gaseous electric discharge device comprising a container, electrodes sealed therein, a gaseous atmosphere therein, and a quantity of vaporizable material therein which emits visible and ultra-violet light when excited to luminescence by an electric discharge between said electrodes, said container consisting of two glass layers fused to each other, the inner layer being thinner than the outer layer and consisting of a glass inert to said vaporizable material and which transmits ultra-violet rays at a wave length of 280 millimicrons and longer and which is opaque to ultraviolet rays of shorter wave length, said glass having the following composition: 58% silica (Si02), 1% boric oxide (B203), 28% alumina (A1203), 8% magnesium oxide (MgO) and 5% calcium oxide (08.0); the outer layer of said container consisting of a borosilicate glass having the following composition: 74% silica (SiOz) 15% boric oxide (B203) 7% sodium oxide (NazO) and 4% alumina (A1203).

3. A gaseous electric discharge device comprising a container, electrodes sealed therein, a gaseous atmosphere therein, and a, quantity of vaporizable material therein which emits visible and ultra-violet light when excited to luminescence by an electric discharge between said electrodes, said container consisting of two glass layers fused to each other, the inner layer being thinner than the outer layer and consisting of a glass inert to said vaporizable material and which transmits ultra-violet rays at a wave length of 280 millimicrons and longer and which is opaque to ultra-violet rays of shorter wave length, said glass having the following composition: 50% silica (S102), 1% boric oxide (B202), 25% alumina (A1203). 8% 7 magnesium oxide (MgO), 6% .calcium oxide (CaO), 5% barium oxide (BaO), and 5% phosphorous pentoxide (P205) the outer layer of said container consisting of a borosilicate glass having the following composition: 75.5% silica (S102), 13.5% boric oxide (B201), 9% sodium oxide (No.20) and 2% alumina (A1202).

HERMANN KREFFT.

KURT LARCHE.

MAX THOMAS. 

